Generally, semiconductor devices include a plurality of circuits which form an integrated circuit fabricated on a semiconductor substrate. A complex network of signal paths will normally be routed to connect the circuit elements distributed on the surface of the substrate. Efficient routing of these signals across the device requires formation of multilevel or multilayered schemes, such as, for example, single or dual damascene wiring structures. The wiring structure typically includes copper, Cu, since Cu based interconnects provide higher speed signal transmission between large numbers of transistors on a complex semiconductor chip as compared with aluminum, Al, -based interconnects.
Within a typical interconnect structure, metal vias run perpendicular to the semiconductor substrate and metal lines run parallel to the semiconductor substrate. Further enhancement of the signal speed and reduction of signals in adjacent metal lines (known as “crosstalk”) are achieved in today's IC product chips by embedding the metal lines and metal vias (e.g., conductive features) in a dielectric material having a dielectric constant of less than silicon dioxide.
One major problem with prior art interconnect structures is that the conductive material within the conductive region has a low electromigration resistance due to a high number of electromigration paths inside the conductive region. The high number of paths is believed to be a result of the microstructure and the average grain size of the conductive material. As is known to those skilled in the art, electromigration is predominately driven by (1) interface diffusion between the conductive material and the dielectric cap, and (2) bulk diffusion along the grain boundaries of the conductive material. The electromigration problem is expected to increase in future semiconductor technologies due to the scaling of such devices.
In view of the above-mentioned electromigration problem with prior art interconnect structures, there is a continued need to provide interconnect structures where the electromigration has been substantially reduced and/or eliminated.